Studies Of Water-flooding Technologies At Low-permeability Reservoir Of Saling Group

Water injection at Low permeability oilfield has become a piece of world-class puzzle. The local potential damage factors at Low permeability reservoir are provoked by foreign fluids to cause multiple formation damage and bring about plugging,which then reduces the percolation of fluids at reservoirs, enhance the injection pressure of injection wells, decrease the injection capacity, and further reduce the oil well productivity, so it is difficult to build a effective driving system between oil and water wells. The Saertu oil layers at Daqing oilfield belong to a kind of sedimentary exterior sandstone body at delta region. It is a typical low permeability sandstone reservoir, which have definite oil and gas richness and geological reserves. Yet it is difficult to develop this reservoir because of high clay content that causes strong water-sensitivity and velocity sensitivity. On the bases of a lot of data about swelling proof and unplugging for home and abroad low permeability oilfield developmnent by waterflooding, the geologic characteristics of the Saling Group oil layers are overall understood. Then a great many of studies are performed from several aspects as follows to know the feasibility of waterflooding type at oil layers of Saling Group.Aiming at such cases of small interpreted thickness but high productive capacity and of oil-bearing occurrence at some layers of high-resistance interlayer deduced originally, on the bases of refinement of calcium reservoir types and four propertied, electric logs in response well to calcium reservoir lithology are renewed to establish a determination standard of calcium electrical reservoir electrical property. New standards for judging electrical properties within oil-bearing calcium and refining oil-bearing reservoir are established with 5 parameters to identify calcium reservoir such as Microelectrode Amplitude Difference Ratio, Sharpness, and Sound Wave Reversion Degree, Square Wave and Density curves together. The new Standards further refine the oil-bearing series, verify the geological reserves again that is consistent with the pilot performance data well. The precision of calcium judgment at the testing area has been enhanced by 13.2% from 79.6% up to 92.8%. This work further supplement and perfect the operation specifications of reservoir division at Saling Group.The reservoir properties of Saling Group are checked by several instruments as X-ray diffractometer, scanning electron microscope and atomic absorption spectrum, etc.. The Saling Group is a mediately and low porous, low permeable reservoir with high content of clay minerals include smectite, illite and kaolinite,among which the kaolinite has the most content. The grains at core surface arrange relatively compactly at the reservoir. The porosity develops poorly with bad connectivity. Secondary quartz grows on the particle surface. The feldspar particles can easily be eroded. 5 sensitivities of Saling Group cores are evaluated in lab according to the Experimental Sequence Industry Standard of Sandstone Reservoir Sensibility Evaluation. The Saling Group is a kind of strong water-sensitivity, partly strong velocity-sensitivity, strong salt-sensitivity, Moderate apt to strong acid-sensitivity, inferior pressure-sensitivity. In the process of waterflooding, the damage caused by strong water-sensitivity and partly strong velocity-sensitivity should be good dealt with.The valid content, swelling proof ratio and dissolution ratio of different types of clay stabilizer are measured by methods of Kjeldahl Nitrogen determination, centrifuging and static weight loss aspectly. The interplanar distances of Ca-smectite before and after soak by clay stabilizers, saturation by glycol vapor and water cleaning are measured by X-ray diffraction method in lab. The antiswelling effect is evaluated further by core flow experiments to optimize the optimal injection rate and period of the antiswelling agent. And the adsorptive retention is measured by static adsorptive process. The conclusions gained from the comparative analysis with the experimental results are as follows: DNT-14 is a type of clay stabilizer of potassium chloride with favorable performance index; its optimum concentration is 3.0%; it is well compatible with formation water and/or the optimized unplugging formulation system; it reduces the degree of the clay swelling by itself to the maximum; it is difficult to be replaced by water molecules or organic molecules; it has strong capacity against water washing; it has less static adsorption; its optimum intake volume and injection period are the same as 5～10PV.The unplugging formulation for the Saling Group is optimized by evaluation of erosion ratio and breaking ration of cores and from modeling experiments with long and short cores in lab, which is 12%HCl+0.5%HF +0.5%HBF4+3%CH3COOH. The principal features of the unplugging fluid system are as follows:①it could preferably increase cores' permeability and keep the cores' intensity and integrality;②its good performance of reaction velocity reduction could effectively decrease the reaction rate of acid-rock to increase the acerbic range to achieve deep acidification;③The clay stabilizer, corrosion inhibitor Fe-stabilizer in the acid system have good effect for acid residue prevention, and every component and the mixture ratio in the acid system are reasonable which could effectively reduce the secondary damage in the process of acidization and fit for the site operation.Aiming at the early production wells at the testing area that could not produce continuously for bad flowing capacity, on the bases of a successful flow limited fracturing and post evaluation of reservoir productivity and fluid properties for a well, in combination with the reservoir properties, the questions about reservoir sensitivities and propping agent incrustation are solved in the process of fracturing from 3 aspects as fracturing fluid system, propping agent system and fracturing technology. A new fracturing technology is put forward.Based on the results in lab, waterflooding field test was carried out under conditions of diffirent clay stabilizer concentration at the Saling Group reservoir. And the optimum concentration of the clay stabilizer in injection water was decided.In these studies, a series of technologies such as the fine geologic research, antiswelling fracture, unplugging with composite acids and correlated waterflooding methods have become a new system for the development by waterflooding at the Saling Group with "5 sensitivities". The practice proves that it is feasible for the Saling Group to be developed by waterflooding with water recovery of about 15%. This technological system has good potential and prospect for application at the La-Sa-Xing oilfield in Daqing.